This is the first successful Sparrowhawk attack I've seen. I've seen three others, all failures - two blackbirds, and a group of redpoll, siskin etc gathered around feeders.
I've quite often seen piles of feathers, but this is the first time I can say for sure that I know WHODUNNIT!

I once saw a sparrowhawk rush over a back garden I was in, across a small field and then through a hole on a large hedge -at great speed. No sooner had it passed through the gap in the hedge than there was an explosion of racing pigeons on the other side. I wasnt aware of the presence of the pigeon loft behind the hedge but the hawk did and seemed to be using surprise attack tactics. Very impressive.